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adopted for the H. P. cylinder, packed with flat rings, but dis-
tributing steam like a D valve. To save space two piston valves c
are supplied to the I. P. cylinder, as seen by the valve rods 3 and
4, connected at their lower ends by the strong crosshead 5; and
the L. P. valve d is double-ported, while being relieved on its
back by the hollow piston h. Piston £", with steam pressure
underneath, supports the weight of valve //, and the L P. valves
are similarly supported by pistons within x and w. Relief valves
UU) on the cylinder covers, are wing valves weighted with springs,
serving as safety outlets for condensation water, which might
otherwise break the covers when the pistons moved. The H. P.
and I. P. slide valves, being vertically above the crank shaft, their
eccentrics are set to lead the cranks, but the L. P. valve is moved
by the rocking lever Q R, and its eccentrics must therefore follow
their crank (see p. 646). The radius link is formed of two
plates, having the die between and the eccentric rods outside,
thus enabling the pin centres to be coincident when in full
gear. The steam reversing cylinder / has its rod u coupled to
the weigh bar lever spy which, through the drag link qr, moves
the link r to fore or aft positions; expansive adjustment is given
by the screw q, and 9 is the valve lever for cylinder /. The
exhaust steam passes to condenser v through standard K ; and air
pump x and circulating pump w are worked from crosshead v by
levers jlk. 7 and 8 are oil pumps, and 6 an oil reservoir with
gauge. The cylinders are jacketed at sides, top, and bottom;
and drains connect to tanks which shew the water used.

Condensers.—The advantages of condensation having been
discussed theoretically, we will now describe the three principal
methods of realising those advantages practically.

The Jet Condenser, Fig. 668, applied to most land engines,
consists of the condenser A, where exhaust steam E is met by a
constant spray of cold water from injection cock G; the air pump
B, worked from the engine piston rod; and the hot well c, from
which the condensed steam and water is taken to feed the boiler.
In order to make B'S action continuous, there, is a suction valve s
and a delivery valve D at each end of the cylinder.

The Surface Condenser; Fig. 669, avoids the mixing of cooling
water with the stearn directly. Formerly, if such water were dirty